a machine that takes over the duty of name resolution and forwarding of SMTP messages for another SMTP server
a mail server is used to deliver your mail and is also called a mail relay
a mail server that is able to determine the appropriate destination SMTP server that it must connect to in order to send a message to a particular recipient
a mail server which will send out all the email, most of the times this will be your ISP's mail server
an SMTP server that receives mail from your mail server and then does its own DNS queries to find the mail server responsible for messages to the destination domain
an SMTP server with the permissions to relay outgoing e-mail messages directly to the Internet from internal SMTP servers
a remote server to which the Exchange server can transmit messages intended for a particular remote domain or routing group
a server or mail process that handles the delivery of Internet mail
a server that will handle delivering all your mail for you
A computer that has more complete information about the entire mail network than do local hosts. Mail addressed to hosts or users unknown to a local host can be forwarded to the smart host over the badhosts or badusers channels.
smart host - A designated server through which Exchange routes all outgoing messages. The smart host then makes the remote connection. If a smart host is designated, the Exchange server only needs to transmit to the smart host, instead of repeatedly contacting the domain until a connection is made. Also known as a relay host.
A smart host is a type of mail relay server which allows an SMTP server to route e-mail to an intermediate mail server rather than directly to the recipient’s server. Often this smart host requires authentication from the sender to verify that the sender has privileges to have mail forwarded through the smart host. This is an important distinction from an open relay that will forward mail from the sender without authentication.